Countries around the world continue to implement safety improvements and corrective actions based on lessons learnt from the 11 March 2011 accident at the Fukushima Daiichi nuclear power plant. This report provides a high-level summary and update on these activities, and outlines further lessons learnt and challenges identified for future consideration. It focuses on actions taken by NEA committees and NEA member countries, and as such is complementary to reports produced by other international organisations.

It is in a spirit of openness and transparency that NEA member countries share this information to illustrate that appropriate actions are being taken to maintain and enhance the level of safety at their nuclear facilities. Nuclear power plants are safer today because of these actions. High priority follow-on items identified by NEA committees are provided to assist countries in continuously benchmarking and improving their nuclear safety practices.

Defence in depth (DiD) is a concept that has been used for many years alongside tools to optimise nuclear safety in reactor design, assessment and regulation. The 2011 Fukushima Daiichi nuclear power plant accident provided unique insight into nuclear safety issues and raised questions about the tools used at nuclear power plants, including the effectiveness of the DiD concept, and whether DiD can be enhanced and its implementation improved.

This regulatory guidance booklet examines and provides advice on the implementation of DiD. A key observation is that the use of the DiD concept remains valid after the Fukushima Daiichi accident. Indeed, lessons learnt from the accident, and the accident?s impact on the use of DiD, have reinforced the fundamental importance of DiD in ensuring adequate safety.

This report is intended primarily for nuclear regulatory bodies, although information included herein is expected to be of interest to licensees, nuclear industry organisations and the general public.

The fundamental objective of all nuclear safety regulatory bodies is to ensure that activities related to the peaceful use of nuclear energy are carried out in a safe manner within their respective countries. In order to effectively achieve this objective, the nuclear regulatory body requires specific characteristics, one of which is a healthy safety culture.

This regulatory guidance report describes five principles that support the safety culture of an effective nuclear regulatory body. These principles concern leadership for safety, individual responsibility and accountability, co-operation and open communication, a holistic approach, and continuous improvement, learning and self-assessment.

The report also addresses some of the challenges to a regulatory body's safety culture that must be recognised, understood and overcome. It provides a unique resource to countries with existing, mature regulators and can be used for benchmarking as well as for training and developing staff. It will also be useful for new entrant countries in the process of developing and maintaining an effective nuclear safety regulator.

Both national and international organisations agree that the fundamental objective of all nuclear safety regulatory bodies -- the regulator's prime purpose -- is to ensure that nuclear licensees operate their facilities at all times in a safe manner. Much has been written about ways to improve regulatory processes or to improve the effectiveness of a regulatory body, including in previous OECD/NEA regulatory guidance booklets. But until now, none have focused on the characteristics of an effective nuclear safety regulator.

Effective organisations are those that have good leadership and are able to transform strategic direction into operational programmes. Effectiveness is about how well the organisation is achieving its fundamental purpose -- in the case of a nuclear safety regulator, ensuring that licensees operate their facilities and discharge their obligations in a safe manner.

This regulatory guidance booklet describes the characteristics of an effective nuclear safety regulator in terms of roles and responsibilities, principles and attributes. Each of the characteristics discussed in this report is a necessary feature of an effective nuclear safety regulator but no one characteristic is sufficient on its own. It is the combination of these characteristics that leads to the effectiveness of a nuclear regulatory body. The report provides a unique resource to countries with existing, mature regulators and can be used for benchmarking as well as training and developing staff. It will also be useful for new entrant countries in the process of developing and maintaining an effective nuclear safety regulator.

As all safety systems in the majority of existing nuclear power plants use the preferred power supply, any voltage surges in these systems could lead to common-cause failures. In the event of an unusual electrical system transient, it is essential that safety-related equipment be isolated or protected from the fault in order to ensure its ability to safely shut down the reactor and remove decay heat.
Based on the analysis of the voltage surges observed at Forsmark-1 in 2006 and Olkiluoto-1 in 2008, this technical opinion paper summarises the current state of knowledge of in-plant and external grid-related challenges to nuclear power plant safety-related electrical equipment. It will be of particular interest to nuclear safety regulators, nuclear power plant operators and grid system regulators and operators.

As manifested by an increasingly globalised media, a nuclear accident anywhere quickly becomes a potential concern for people everywhere. It is therefore of prime importance that nuclear regulators’ communication strategies take into consideration the expectations and concerns of the public and provide sound information not only for the people of the affected country, but also for citizens worldwide. Public trust is a key element in being able to do so effectively and of particular importance when there are consequences for people or the environment. International co-operation can play a fundamental role in helping to improve crisis communication on national and global scales in the event of a nuclear accident or radiological emergency. These proceedings contain the papers, recommendations and conclusions of the workshop, which was attended by over 180 experts from 27 countries and 6 international organisations.

This report outlines the response of the OECD Nuclear Energy Agency (NEA) and its member countries to the March 2011 accident at TEPCO's Fukushima Daiichi nuclear power plant. All NEA members took early action to ensure and confirm the continued safety of their nuclear power plants and the protection of the public. Consistent with its objective of maintaining and further developing the scientific, technological and legal bases for safe nuclear energy, the NEA has assisted its member countries in their individual and collective responses to the accident. It has also provided direct assistance to the relevant authorities in Japan. These actions are summarised in the report along with lessons learnt thus far. Key messages are offered as a means to help strengthen the basis for nuclear safety and its implementation in all countries using nuclear power.

The way in which nuclear licensees’ organisations are structured and resourced clearly has a potential impact on nuclear safety. As experience has continually demonstrated, operating organisations with a strong training programme for personnel, adequate resourcing and overall effective leadership and management perform more effectively in times of crisis than those lacking in one or more of these areas. In parallel, the nuclear industry is developing new resource deployment strategies which are making increased use of contractors and leading to changes in organisational structure, which in turn create challenges for the continued safe operation of nuclear facilities. This technical opinion paper represents the consensus among human and organisational factor specialists in NEA member and associated countries on the methods, approaches and good practices to be followed in designing an organisation with a strong safety focus while meeting business needs. It also considers some of the attributes that an organisation which is effectively managing its resources and capabilities might demonstrate.

Managing the ageing of fuel cycle facilities (FCFs) means, as for other nuclear installations, ensuring the availability of required safety functions throughout their service life while taking into account the changes that occur with time and use. This technical opinion paper identifies a set of good practices by benchmarking strategies and good practices on coping with physical ageing and obsolescence from the facility design stage until decommissioning. It should be of particular interest to nuclear safety regulators, fuel cycle facilities operators and fuel cycle researchers.

Nuclear power reactors have become a major source of electricity supply in many countries and, based on the experience of safe and reliable operation, many operators have sought and received authorisation for long-term operation beyond the period assumed in the plant’s design. Acceptance of a nuclear power plant for long-term operation must be based on evidence that the plant will operate safely over the extended period of service. This requires an assessment of the current and projected condition of the plant and, in particular, of the systems that perform fundamental safety functions, to ensure that these systems will continue to perform their safety functions during the extended operating period. Programmes for long-term operation must be informed by operating experience and must also consider and assess environmental impacts.
This guidance document is intended to assist regulatory organisations in assessing and approving the long-term operation safety assessments submitted by operators. It outlines the fundamental principles that should govern decisions on authorisation for long-term operation. It also describes regulatory challenges and considerations that may arise in an assessment of a plant for long-term operation.

Computational fluid dynamics (CFD) is increasingly being adopted in nuclear reactor safety (NRS) analyses as a tool which enables a better description of specific safety-relevant phenomena occurring in nuclear reactors. The OECD Nuclear Energy Agency (NEA) Committee on the Safety of Nuclear Installations (CSNI) has in recent years conducted important activities in the CFD area, including the organisation of three workshops. The CFD4NRS-3 workshop was the third in the series and was held in Bethesda, Maryland, USA on 14-16 September 2010. A total of 200 experts participated. These proceedings contain the 4 keynote lectures, including the synthesis of results for the Tee-junction Benchmark, and the 57 technical papers presented at the workshop.

One of the major achievements of the OECD Nuclear Energy Agency (NEA) is the knowledge it has helped to generate through the organisation of joint international research projects. Such projects, primarily in the areas of nuclear safety and radioactive waste management, enable interested countries, on a cost-sharing basis, to pursue research or the sharing of data with respect to particular areas or issues. Over the years, more than 30 joint projects have been conducted with wide participation of member countries.
The purpose of this report is to describe the achievements of the OECD/NEA joint projects on nuclear safety research that have been carried out over the past three decades, with a particular focus on thermal-hydraulics, fuel behaviour and severe accidents. It shows that the resolution of specific safety issues in these areas has greatly benefited from the joint projects’ activities and results. It also highlights the added value of international co-operation for maintaining unique experimental infrastructure, preserving skills and generating new knowledge.

Most of the current nuclear fuel safety criteria were established during the 1960s and early 1970s. Although these criteria were validated against experiments with fuel designs available at that time, a number of tests were based on unirradiated fuels. Additional verification was performed as these designs evolved, but mostly with the aim of showing that the new designs adequately complied with existing criteria, and not to establish new limits.

In 1996, the OECD Nuclear Energy Agency (NEA) reviewed existing fuel safety criteria, focusing on new fuel and core designs, new cladding materials and industry manufacturing processes. The results were published in the Nuclear Fuel Safety Criteria Technical Review of 2001. The NEA has since re-examined the criteria. A brief description of each criterion and its rationale are presented in this second edition, which will be of interest to both regulators and industry (fuel vendors, utilities).

The application of lessons learnt from the International Reporting System for Operating Experience (IRS) is an essential element for enhancing the safe operation of nuclear power plants (NPPs) throughout the world. The IRS provides a mechanism for the exchange of information related to the incident, actions taken, root cause analysis and lessons learnt. This feedback on how to adequately remedy, or avoid, possible challenges and precursors is of paramount importance to operational safety. The IRS improves international awareness of potential challenges, actual incidents and “precursors” in NPP operations. The heightened awareness generated by feedback from operating experience has resulted in numerous improvements to equipment, procedures and training in many NPPs. The application of operational feedback also benefits the design of the next generation of NPPs. Operating experience has demonstrated that design modification issues documented in IRS reports can have a significant impact on safety. The IRS is jointly operated and managed by the OECD Nuclear Energy Agency (OECD/NEA) and the International Atomic Energy Agency (IAEA).

Acceptance criteria for emergency core cooling systems (ECCS) define the maximum temperature and degree of oxidation in order to avoid excessive embrittlement and hence failure of the fuel cladding, which would affect core cooling in the case of a loss-of-coolant accident (LOCA). The criteria are mainly based on experimental data obtained in the 1970s-80s. Several types of tests have been performed to evaluate structural integrity and embrittlement of the cladding under LOCA conditions, and consequently different test methodologies have been used for determining the cladding embrittlement criteria. The current trend towards high burn-up and the use of new cladding alloys has increased the need for international discussions on these test methodologies and acceptance criteria. In response, the NEA Committee on the Safety of Nuclear Installations (CSNI) and its Working Group on Fuel Safety produced this technical opinion paper, which should be of particular interest to nuclear safety regulators, nuclear power plant operators and fuel researchers.

This report provides an overview of experimental facilities that can be used to carry out nuclear safety research for sodium fast reactors and identifies priorities for organising international co-operative programmes at selected facilities. The information has been collected and analysed by a Task Group on Advanced Reactor Experimental Facilities (TAREF) as part of an ongoing initiative of the NEA Committee on the Safety of Nuclear Installations (CSNI) which aims to define and to implement a strategy for the efficient utilisation of facilities and resources for Generation IV reactor systems.

A common theme throughout the series of NEA regulatory guidance reports, or “green booklets”, is the premise that the fundamental objective of all nuclear safety regulatory bodies is to ensure that nuclear facilities are continuously maintained and operated in an acceptably safe manner. In meeting this objective the regulator must bear in mind that it is the operator that has responsibility for safely operating the nuclear facility; the role of the regulator is to assess and to provide assurance regarding the operator’s activities in terms of assuming that responsibility.
The full series of these reports was brought together in one edition for the first time in 2009 and was widely found to be a useful resource. This second edition comprises 14 volumes, including the latest on The Nuclear Regulator's Role in Assessing Licensee Oversight of Vendor and Other Contracted Services. The reports address various challenges that could apply throughout the lifetime of a nuclear facility, including design, siting, manufacturing, construction, commissioning, operation, maintenance and decommissioning. The compilation is intended to serve as a knowledge management tool both for current regulators and the new nuclear professionals and organisations entering the regulatory field.

Contracted services are an integral part of the design, construction and operation of a nuclear facility. Changes in the nuclear industry sector, including varied availability of nuclear expertise, the expansion of the international supply market and the introduction of new technologies, have tended to increase licensees’ use of contracted services. These changes have created challenges for licensees and regulators related to the retention of nuclear expertise, the effective management of the interfaces between the licensees and contractors, and the oversight of contractor manufacturing quality in the context of greater multinational diversity. The regulatory body must address these challenges to provide assurance that the licensees maintain their responsibility for the safety of the facilities, regardless of who provides goods and services or where the activities involved in the supply chain take place. This report is intended to assist regulatory bodies in assessing their current practices for the regulatory oversight of licensees’ use of contractors, and adapting them where necessary to meet the evolving situation.

Computational fluid dynamics (CFD) is to an increasing extent being adopted in nuclear reactor safety (NRS) analyses as a tool that enables a better description of specific safety-relevant phenomena occurring in nuclear reactors. The NEA Committee on the Safety of Nuclear Installations (CSNI) has in recent years conducted important activities in the CFD area, including the organisation of two workshops. The “XCFD4NRS” workshop was the second in the series and was held in Grenoble, France in September 2008. A total of 147 experts from 22 countries took part. These proceedings contain the five keynote lectures, summaries of the activities of three CFD writing groups and the 59 technical papers presented at the workshop.

Considerable experimental and analytical work has been performed in recent years which has led to a broader and deeper understanding of phenomena related to reactivity-initiated accidents (RIAs). Further, newly designed fuels – such as mixed-oxide (MOX) fuel and rods with new cladding – have been introduced which might behave differently than those used previously, both under normal operating conditions and during transients. Compared with 20 years ago, fuel burn-up has been significantly increased. These and other factors have led the NEA Committee on the Safety of Nuclear Installations (CSNI) and its Working Group on Fuel Safety to produce this state-of-the-art report. The report should be of particular interest to nuclear safety regulators, nuclear plant operators and fuel researchers.

Nuclear power plant modifications may be needed for a number of different reasons. These include physical ageing of plant systems, structures and components; obsolescence in hardware and software; feedback from operating experience; and opportunities for improved plant safety, reliability or capability. However, experience has also shown that weaknesses in the design and/or implementation of modifications can present significant challenges to plant safety. They can also have a considerable impact on the commercial performance of the plant. It is therefore important that the plant modification process reflect a recognition of the potential impact of human errors and that it incorporate suitable measures to minimise the potential for such errors.

In this context, the NEA Committee on the Safety of Nuclear Installations (CSNI) and its Working Group on Human and Organisational Factors organised an international workshop in 2003 to discuss the role of human and organisational performance in the nuclear plant modification process. This technical opinion paper represents the consensus of specialists in human and organisational factors (HOF) in the NEA member countries on commendable practices and approaches to dealing with nuclear plant modifications. It considers factors that should be taken into account when developing a modification process and identifies some lessons learnt from application of the process. The paper should be of particular interest of nuclear safety regulators and nuclear power plant operators.

Errors during maintenance and periodic testing are significant contributors to plant events. These errors may not always be revealed by post-maintenance tests and may remain undetected for extended periods until the affected system is called upon to function. It is therefore important that the plant maintenance process take into account the potential impact of human and organisational errors, and that it incorporate suitable measures to minimise the potential for such errors.

The NEA Committee on the Safety of Nuclear Installations (CSNI) and its Working Group on Human and Organisational Factors organised an international workshop to discuss the role of human and organisational performance on maintenance. This technical opinion paper represents the consensus of specialists on human and organisational factors in NEA member countries on commendable practices and approaches to dealing with nuclear power plant maintenance. It sets out a framework for including a systematic consideration of human and organisational factors in the plant maintenance process. The paper should be of particular interest to nuclear safety regulators and nuclear power plant operators.

It is a dynamic time for the nuclear power sector. Existing reactor control rooms are undergoing various forms of modernisation. New reactors are being built in many countries and advanced reactors are being designed through international co-operation to support power generation for decades to come. The new technologies and concepts that are being considered in this context could impact upon the roles of the plant operators and thus plant safety. It is therefore important that the potential implications – both positive and negative – are evaluated and understood.

Through this technical opinion paper, the NEA Committee on the Safety of Nuclear Installations (CSNI) has sought to identify a set of research topics that should be explored in order to enhance knowledge of the human and organisational factors concerned. Research to address the topics described in this paper will provide the technical basis to help ensure that the benefits of new technology are realised and that the potential negative effects are minimised.

This paper should be of particular interest to research organisations and other stakeholders (including regulatory agencies, international organisations and industry organisations) that could support this research and benefit from its results.

This report provides an overview of experimental facilities that can be used to carry out nuclear safety research for gas-cooled reactors and identifies priorities for organising international co-operative programmes at selected facilities. The information has been collected and analysed by a Task Group on Advanced Reactor Experimental Facilities (TAREF) as part of an ongoing initiative of the NEA Committee on the Safety of Nuclear Installations (CSNI) which aims to define and to implement a strategy for the efficient utilisation of facilities and resources for Generation IV reactor systems.

A common theme throughout the series of NEA regulatory guidance reports, or “green booklets”, is the premise that the fundamental objective of all nuclear safety regulatory bodies is to ensure that nuclear facilities are operated at all times and later decommissioned in an acceptably safe manner. In meeting this objective the regulator must keep in mind that it is the operator that has responsibility for safely operating a nuclear facility; the role of the regulator is to oversee the operator’s activities as related to assuming that responsibility.

For the first time, the full series of these reports have been brought together in one edition. As such, it is intended to serve as a knowledge management tool both for current regulators and the younger generation of nuclear experts entering the regulatory field. While the audience for this publication is primarily nuclear regulators, the information and ideas may also be of interest to nuclear operators, other nuclear industry organisations and the general public.

Considerable experimental and analytical work has been performed in recent years which has led to a broader and deeper understanding of phenomena related to loss-of-coolant accidents (LOCAs). Further, new cladding alloys have been produced, which might behave differently than the previously used Zircaloy-4, both under normal operating conditions and during transients. Compared with 20 years ago, fuel burn-up has been significantly increased. These and other factors have led the NEA Committee on the Safety of Nuclear Installations (CSNI) and its Working Group on Fuel Safety to produce this state-of-the-art report. The report should be of particular interest to nuclear safety regulators, nuclear power plant operators and nuclear fuel researchers.

The NEA Committee on the Safety of Nuclear Installations (CSNI) has recently completed a study on the availability and utilisation of facilities supporting safety studies for current and advanced nuclear power reactors. The study showed that significant steps had been undertaken in the past several years in support of safety test facilities, mainly by conducting multinational joint projects centered on the capability of unique test facilities worldwide.

Given the positive experience of the safety research projects, it has been recommended that efforts be made to prioritise technical issues associated with advanced (Generation IV) reactor designs and to develop options on how to efficiently obtain the necessary data through internationally co-ordinated research, preparing a gradual extension of safety research beyond the needs set by currently operating reactors.

This statement constitutes a reference for future CSNI activities and for safety authorities, R&D centres and industry for internationally co-ordinated research initiatives in the nuclear safety research area.

The fundamental objective of all nuclear safety regulatory bodies is to ensure that nuclear facilities are operated, as well as decommissioned, in an acceptably safe manner. However, in meeting this objective the regulator must keep in mind that it is the operator that has responsibility for safely operating a nuclear facility; the role of the regulator is to oversee the operator’s activities as related to assuming that responsibility.

There are currently many sources of information available to the regulator pertaining to safety at any given nuclear facility, such as inspection reports, operating experience reports, research results, periodic safety reviews, probabilistic safety analysis (PSA) results, insights from IAEA reviews and other similar information. A major challenge for the regulator is to systematically collect and analyse this information in order to arrive at an integrated assessment of the level of safety of the particular facility and then to make a judgement about its acceptability. In order to assist member countries in addressing this challenging question, the Committee on Nuclear Regulatory Activities (CNRA) of the OECD Nuclear Energy Agency (NEA) has sponsored this report.

The primary focus of the report is on how the regulatory body can systematically collect and make an integrated analysis of all the relevant safety information available to it and arrive at a sound judgement on the acceptability of the level of safety of the facilities that it regulates. It therefore follows that the target audience for this report is primarily nuclear regulators, although the information and ideas may also be of interest to nuclear operators, other nuclear industry organisations and segments of civil society.

This workshop enabled the exchange of experience among regulators, research managers and industry on the needs, priorities and foreseeable trends for nuclear safety research in a regulatory context. It also addressed the means that are or can be used for effectively performing such research.

The presentations highlighted priority safety issues, at present and in the near term, for operating plants and new reactors. During the workshop, participants discussed the challenges that the nuclear community will face in the long term for performing safety evaluations of advanced reactor designs, and explored various avenues for organising the research and infrastructure that will be needed.

These proceedings will be of particular interest to nuclear specialists and research managers wishing to obtain an international perspective of current and foreseeable needs in regulatory-driven nuclear safety research.

On 5-7 September 2006, the OECD Nuclear Energy Agency organised a workshop on Benchmarking of CFD Codes for Application to Nuclear Reactor Safety (CFD4NRS) in co-operation with the International Atomic Energy Agency. The workshop was hosted in Germany by the Gesellschaft für Anlagen und Reaktorsicherheit (GRS). The purpose of the workshop was to provide a forum for numerical analysts and experimentalists to exchange information on nuclear reactor safety activities relevant to computational fluid dynamics (CFD) validation, with the objective of providing input to create a practical, state-of-the-art, web-based assessment matrix on the use of CFD for nuclear reactor safety applications. These proceedings contain the 39 technical papers presented at the workshop, which was attended by 100 participants.

This technical opinion paper represents the consensus of risk analysts in NEA member countries on the current state of the art of level-2 probabilistic safety assessment (PSA) and its applications in accident management of nuclear power plants. Level-2 PSA models the phenomena that could occur following the onset of core damage that have the potential to challenge the containment integrity and lead to a release of radioactive material to the environment. The paper's objective is to present decision makers in the nuclear field with a clear technical opinion on the status as implemented in industrial PSAs.

The intended audience is primarily nuclear safety regulators, researchers and industry representatives dealing with safety management and severe accidents. Government authorities and nuclear power plant operators may also be interested in the paper.

Uncertainty in relation to several severe accident phenomena plays a major role in probabilistic safety analyses involving beyond-design-basis accident scenarios for nuclear power plants. The technical papers presented herein will be valuable for nuclear safety analysts, nuclear power plant designers and R&D managers, especially with regard to unresolved severe accident issues or issues where risk uncertainty is high.

This report provides an overview of experimental facilities that can be used to address nuclear safety research issues in OECD member countries, and identifies priorities for organising international co-operative programmes centred on selected facilities. The information has been gathered and analysed by a Senior Group of Experts on Nuclear Safety Research, in the context of an ongoing initiative of the NEA Committee on the Safety of Nuclear Installations (CSNI) aimed at maintaining critical experimental infrastructure for nuclear safety studies in member countries.

One of the main missions of nuclear regulators is to protect the public, and this cannot be completely achieved without public confidence. The more a regulatory process is transparent, the more such confidence will grow. Despite important cultural differences across countries, a number of common features characterise media and public expectations regarding any activity with an associated risk.

A common understanding of transparency and main stakeholders' expectations in the field of nuclear safety were identified during this workshop, together with a number of conditions and practices aimed at improving the transparency of nuclear regulatory activities. These conditions and practices are described herein, and will be of particular interest to all those working in the nuclear regulatory field. Their implementation may, however, differ from one country to another depending on national context.

An important factor for public confidence in the nuclear regulator is the general public trust of the government and its representatives, which is clearly not the same in all countries. Likewise, cultural differences between countries can be considerable, and similar means of communication between government authorities and the public may not be universally effective.

Nevertheless, this workshop identified a number of common principles for the communication of nuclear regulatory decisions that can be recommended to all regulators. They have been cited in particular for their ability to help build, measure and/or improve overall public confidence in the nuclear regulator.

Nuclear regulatory self-assessment together with the benchmarking of regulatory practices against those of other countries operating nuclear power plants are key elements in maintaining a high level of nuclear safety. In that light, the Spanish Consejo de Seguridad Nuclear (CSN) formally asked the OECD Nuclear Energy Agency (NEA) to establish an international peer review team to assess the CSN report on the lessons learnt as a result of the 2004 Vandellós II event involving essential service water system degradation.

The International Review Team considers the CSN report prepared in follow-up to the Vandellós event to be a commendable effort in regulatory self-assessment. The report, complemented by this international peer review, should enable the CSN to take appropriate action to ensure that its regulatory supervision is in line with best international practice.

The Incident Reporting System (IRS) is an essential element of the international operating experience feedback system for nuclear power plants. The IRS is jointly operated and managed by the Nuclear Energy Agency (NEA), a semi-autonomous body within the Organisation for Economic Co-operation and Development (OECD), and the International Atomic Energy Agency (IAEA), a specialised agency within the United Nations System.

The fundamental objective of all nuclear safety regulatory bodies is to ensure that nuclear utilities operate their plants in an acceptably safe manner at all times. Learning from experience has been a key element in meeting this objective. It is therefore very important for nuclear power plant operators to have an active programme for collecting, analysing and acting on the lessons of operating experience that could affect the safety of their plants.

NEA experts have noted that almost all of the recent, significant events reported at international meetings have occurred earlier in one form or another. Counter-actions are usually well-known, but information does not always seem to reach end users, or corrective action programmes are not always rigorously applied. Thus, one of the challenges that needs to be met in order to maintain good operational safety performance is to ensure that operating experience is promptly reported to established reporting systems, preferably international in order to benefit from a larger base of experience, and that the lessons from operating experience are actually used to promote safety.

This report focuses on how regulatory bodies can ensure that operating experience is used effectively to promote the safety of nuclear power plants. While directed at nuclear power plants, the principles in this report may apply to other nuclear facilities as well.

Probabilistic safety analyses (PSAs) for many of the nuclear power plants throughout the world are being maintained as "living PSAs" (LPSAs), being updated to take account of changes to the design and operation of the plant, improvements in the understanding of how the plant behaves in fault situations and improved PSA methods, models and data. One of the specific applications of a living PSA is the risk monitor, used by operators and regulators to provide risk information employed in the decision-making process to ensure the safe operation of nuclear power plants. Since the first risk monitors were put into operation in 1988, the number of risk monitors worldwide has increased rapidly. By the end of 2003 there were more than 110 in operation and this figure should increase to over 150 when those monitors being developed are placed in service.

Combining these two technical opinion papers into a single publication provides the reader - notably senior researchers and industry leaders, nuclear safety regulators, nuclear power plant operators - with a concise assessment of the current state of the art, thus enabling better analysis when evaluating proposals or the development of these applications.

The mission of the Committee on Nuclear Regulatory Activities (CNRA) and the Committee on the Safety of Nuclear Installations (CSNI) is to assist member countries in maintaining and further developing the knowledge, competence and infrastructure needed to support the safe operation of nuclear power plants and fuel cycle facilities throughout their life cycle, as well as their efficient and effective regulation based upon sound technical information, shared experience and up-to-date methods.

The fundamental objective of all nuclear safety regulatory bodies is to ensure that nuclear utilities operate their plants at all times in an acceptably safe manner. In meeting this objective, the regulatory body should strive to ensure that its regulatory decisions are technically sound, consistent from case to case, and timely. In addition, the regulator must be aware that its decisions and the circumstances surrounding those decisions can affect how its stakeholders, such as government policy makers, the industry it regulates, and the public, view it as an effective and credible regulator. In order to maintain the confidence of those stakeholders, the regulator should make sure that its decisions are transparent, have a clear basis in law and regulations, and are seen by impartial observers to be fair to all parties.

Based on the work of a Nuclear Energy Agency (NEA) expert group, this report discusses some of the basic principles and criteria that a regulatory body should consider in making decisions and describes the elements of an integrated framework for regulatory decision making.

This report, prepared by an independent review group, characterises the current role, priorities and working methods of the NEA Committee on Nuclear Regulatory Activities (CNRA), identifies and analyses issues of concern, and suggests ways to further increase the efficiency and effectiveness as well as the visibility of the committee. It also reviews the role and interactions between the CNRA and the other NEA standing technical committees and international organisations, and suggests ways to improve co-ordination and co-operation.

Conclusions and recommendations have been derived concerning the mid-term and long-term role and orientation of the committee and, in particular, the balance between technical- and policy-related activities.

This report, prepared by a senior-level assessment group, describes the current role, priorities and working methods of the NEA Committee on the Safety of Nuclear Installations (CSNI), identifies and analyses issues of concern, and suggests ways to further increase the efficiency and effectiveness of the committee. It also reviews CSNI interactions with the NEA Committee on Nuclear Regulatory Activities (CNRA), the other NEA standing technical committees and international organisations, and suggests ways to improve co-ordination and co-operation. In closing, conclusions are drawn and recommendations made concerning the future operation and role of the committee.

The procurement and preparation of fuel for nuclear power reactors, followed by its recovery, processing and management subsequent to reactor discharge, are frequently referred to as the "front end" and "back end" of the nuclear fuel cycle. The facilities associated with these activities have an extensive and well-documented safety record accumulated over the past 50 years by technical experts and safety authorities. This information has enabled an in-depth analysis of the complete fuel cycle.

Preceded by two previous editions in 1981 and 1993, this new edition of the Safety of the Nuclear Fuel Cycle represents the most up-to-date analysis of the safety aspects of the nuclear fuel cycle. It will be of considerable interest to nuclear safety experts, but also to those wishing to acquire extensive information about the fuel cycle more generally.

This technical opinion paper represents the consensus of risk analysts in NEA member countries on the current state of the art of human reliability analysis (HRA) in probabilistic safety assessment (PSA) for nuclear power plants. The paper's objective is to present decision makers in the nuclear field with a clear technical opinion on HRA status as implemented in industrial PSAs. The intended audience is primarily nuclear safety regulators, senior researchers and industry leaders. Government authorities, nuclear power plant operators and the general public may also be interested.

Nuclear licensees are increasingly required to adapt to a more challenging commercial environment as electricity markets are liberalised. One of the costs that is often perceived as being amenable to control is staffing, and hence there is significant exploration of new strategies for managing this cost - for example, by reducing staffing levels, changing organisational structures, adopting new shift strategies, introducing new technology or increasing the proportion of work carried out by external contractors. However, if changes to staffing levels or organisational structures and systems are inadequately conceived or executed they have the potential to affect the way in which safety is managed.

In this context, the NEA Committee on the Safety of Nuclear Installations (CSNI) and its Special Expert Group on Human and Organisational Factors (SEGHOF) organised an international workshop to discuss the management and regulation of organisational change in 2001. This technical opinion paper distils the findings of that workshop and sets out the factors that regulatory bodies might reasonably expect to be addressed within licensees' arrangements to manage organisational change. The paper should be of particular interest to both regulators and managers of nuclear utilities.

This technical opinion paper provides the reader with a concise description of both the benefits and disadvantages of using probabilistic safety assessment (PSA) to analyse operational events in nuclear power plants in order to facilitate better operator feedback. The paper's objective is to present decision makers in the nuclear field with a clear technical opinion on how PSA techniques can be used to address this issue. The intended audience is primarily nuclear safety regulators, senior researchers and industry leaders. Government authorities, nuclear power plant operators and the general public may also be interested.

The degree to which regulatory-sponsored nuclear safety research is conducted and utilised in the regulatory process varies from country to country. This statement articulates the value to efficient and effective regulation, as well as to safety, of maintaining safety research capability and expertise. It can serve as a guideline for consideration by NEA member countries in determining what safety research capability and expertise should be maintained in support of regulation and why. The intended readership is primarily nuclear safety research managers, regulatory organisations and research centres. Government authorities, nuclear power plant operators and the general public may also be interested.

Under normal operation, nuclear reactor fuel is cooled by water circulating in the primary circuit. In the case of a loss-of-coolant accident, the reactor is stopped automatically. Residual fuel heat must then be evacuated, typically by use of a safety injection system and a reactor containment spray system. These systems are fed with water recovered from the bottom of the containment through sumps. However, because this water may contain debris (insulating material, concrete particles, paint), sumps are equipped with strainers. These strainers may become clogged, preventing emergency coolant recirculation. This could in turn lead to reactor core overheating, or melting in the most extreme cricumstances.

Participants at the workshop discussed the most recent research and developments in this field, as well as proposed and implemented solutions. These proceedings contain the papers presented at the workshop as well as a summary of the discussions that took place.

The desired outcome of nuclear regulatory activities is the safe operation of nuclear facilities in a manner that protects public health and safety, and the environment. The operator has prime responsibility for safe operation; however, the actions of the regulator contribute to this objective.

A task group was established by the NEA Committee on Nuclear Regulatory Activities (CNRA) to develop a set of direct performance indicators of regulatory efficiency and effectiveness. This report describes the pilot project carried out by the task group to test the indicators developed, and makes some general observations about the usefulness of individual indicators as well as recommendations for future activities. While primarily directed at nuclear safety regulators, the report may also be of interest to government authorities, nuclear power plant operators and the general public.

In June 2003, the OECD Nuclear Energy Agency (NEA) Committee on Nuclear Regulatory Activities (CNRA) organised a topical session on the importance of human performance to nuclear safety and the factors influencing it. The discussion focused on three questions:

- Is human performance as important to the safety of nuclear installations as many references seem to indicate?
- Has the importance of human performance increased during the past five to ten years?
- What recommendations can be made on how to manage human peformance challenges?

This publication provides a summary of the introductory presentations as well as a description of the regulatory challenges identified during the discussions. The publication's intended audience is primarily nuclear regulators; it may also be of interest to technical support organisations, nuclear operators, governmental bodies and the general public.

Feedback on operating experience from nuclear power plants is intended to help avoid occurrence or recurrence of safety-significant events. Well-established feedback systems exist on the national and international levels. One such example is the Incident Reporting System (IRS), jointly operated by the International Atomic Energy Agency (IAEA) and the OECD Nuclear Energy Agency (NEA).

This technical opinion paper presents the international systems used to collect operating experience, the role of recurring events within them, examples of recurrence and ideas about how to improve the situation. It is expected that managers in both nuclear utilities and regulatory bodies, persons involved in operating experience feedback and analysis, inspectors and technical support organisation staff will be interested in this publication.

The method for setting nuclear safety research priorities and the criteria for ranking programmes and projects, including for their closure, vary from one country to another. This collective statement addresses good practices in conducting nuclear safety research and focuses on closure considerations. It also considers the effects that closure can have for regulators and the industry, including potential losses of technical capability, expertise and facilities. The intended readership is primarily research managers, regulatory organisations and research centres. Government authorities, nuclear power plant operators and the general public may also be interested.

Incident reporting has become an increasingly important aspect of the operation and regulation of all public health and safety-related industries. Diverse industries such as aeronautics, chemicals, pharmaceuticals and explosives all depend on operating experience to provide lessons learnt about safety.

The Incident Reporting System (IRS) is an essential element of the system for feeding back international operating experience for nuclear power plants. IRS reports contain information on events of safety significance with important lessons learnt. These experiences assist in reducing or eliminating recurrence of events at other plants. The IRS is jointly operated and managed by the Nuclear Energy Agency and the International Atomic Energy Agency (IAEA).

The first report, which covered the period July 1996-June 1999, was widely acclaimed and encouraged both agencies to prepare this second report in order to highlight important lessons learnt from around 300 events reported to the IRS for the period July 1999-December 2002. Several areas were selected in this report to show the range of important topics available in the IRS. These include different types of failure in a variety of plant systems, as well as human performance considerations.

This report is primarily aimed at senior officials in industry and government who have decision-making roles in the nuclear power industry.

Licensee self-assessment (LSA) by nuclear power plant operators is described as all the activities that a licensee performs in order to identify opportunities for improvements. An LSA is part of an organisation's holistic management system, which must include other process elements. Particularly important elements are: a process for choosing which identified potential improvements should be implemented and a process of project management for implementing the improvements chosen. Nuclear regulators expect the licensee to run an effective LSA programme, which reflects the licensee's "priority to safety".

Based on contributions from members of the NEA Committee on Nuclear Regulatory Activities (CNRA), this publicaiton provides an overview of the current regulatory philosophy on and approaches to LSA as performed by licensees. The publication's intended audience is primarily nuclear safety regulators, but government authorities, nuclear power plant operators and the general public may also be interested.

Regulator-industry co-operation in nuclear safety research has potential advantages as well as disadvantages. This report provides research managers in industry, regulatory organisations and research centres with information on current practices in collaborative safety research in OECD member countries. It identifies means of establishing effective industry-regulator collaboration and provides indications on how to overcome difficulties that can arise. It also advises on possible areas of concern. The report addresses in particular the issue of regulator independence, means to preserve it and ways to demonstrate it to the public while undertaking collaboration with industry.

Each nuclear power plant, fuel cycle facility and nuclear research and test facility that is operating today will eventually reach the end of its useful life and cease operation. During the period of its decommissioning, it is important to properly manage the health and environmental hazards and physical protection measures of the shutdown facility in order to protect the health and safety of the public and workers and to safeguard any nuclear materials. In this regard, the nuclear safety regulatory body is responsible for independently assuring that decommissioning activities are conducted safely, that radioactive materials and spent nuclear fuel are disposed of properly and that the site is in an acceptable end state.

The purpose of this report is to describe the broad range of safety, environmental, organisational, human factors and public policy issues that may arise during the decommissioning of nuclear reactors and that the regulatory body should be prepared to deal with in the framework of its national regulatory system. The intended audience is primarily nuclear regulators, although the information and ideas may also be of interest to government authorities, environmental regulators, nuclear operating organisations, technical expert organisations and the general public.

New nuclear reactor designs are expected to have a higher level of safety than current designs. As part of the efforts to achieve this, important safety issues related to the new designs need to be identified at an early stage, and research required for problem resolution defined.

These proceedings bring together the papers presented at the OECD/NEA Workshop on Advanced Nuclear Reactor Safety Issues and Research Needs. Conclusions of the workshop discussions are offered at the end of the book, which will be of particular interest to all those involved in planning and designing the next generation of nuclear reactors.

These technical opinion papers represent the consensus of risk analysts and experts in NEA Member countries on the current state of the art in Fire Probabilistic Safety Assessment (PSA) for nuclear power plant design and operation and Seismic PSA for nuclear facilities. The objective is to present clear technical opinions to decision makers in the nuclear community. As such, the intended audience is primarily nuclear safety regulators, senior researchers and industry leaders. Government authorities, nuclear power plant operators and the general public may also be interested.

The concept of improving nuclear safety versus maintaining it has been discussed at a number of nuclear regulators meetings in recent years. National reports have indicated that there are philosophical differences between NEA member countries about whether their regulatory approaches require licensees to continuously improve nuclear safety or to continuously maintain it. It has been concluded that, while the actual level of safety achieved in all member countries is probably much the same, this is difficult to prove in a quantitative way. In practice, all regulatory approaches require improvements to be made to correct deficiencies and when otherwise warranted.

Based on contributions from members of the NEA Committee on Nuclear Regulatory Activities (CNRA), this publication provides an overview of current nuclear regulatory philosophies and approaches, as well as insights into a selection of public perception issues. This publication's intended audience is primarily nuclear safety regulators, but government authorities, nuclear power plant operators and the general public may also be interested.

The economic pressures of electricity market competition have led nuclear power plant operators to seek ways to increase electricity production and to reduce operating costs at their plants. Corresponding pressures on the regulatory bodies include operator demande to reduce regulatory burdens perceived as unnecessary and general resistance to consider safety backfits sought by the regulator.

The purpose of this report is to describe potential situations giving rise to safety backfit questions and to discuss regulatory approaches for judging the backfits.

The intented audience for this report is primarily nuclear regulators, although the information and ideas may also be of interest to nuclear operating organisations, other industry organisations and the general public.

In many countries, retiring nuclear safety experts are not being replaced by younger counterparts. This risks creating a shortfall in the number of experts available to ensure the effective regulation of the nuclear power industry. It could also result in the loss of much of the present nuclear safety knowledge base. This report discusses specific ways to maintain future nuclear safety competencies in nuclear regulatory authorities and the nuclear industry.

Ensuring that nuclear installations are operated and maintained in such a way that their impact on public health and safety is as low as reasonably practicable has been and will continue to be the cornerstone of nuclear regulation. In the past, nuclear incidents provided the main impetus for regulatory change. Today, economic factors, deregulation, technological advancements, government oversight and the general requirements for openness and accountability are leading regulatory bodies to review their effectiveness. In addition, seeking to enhance the present level of nuclear safety by continuously improving the effectiveness of regulatory bodies is seen as one of the ways to strengthen public confidence in the regulatory systems.

This report covers the basic concepts underlying nuclear regulatory effectiveness, advances being made and future requirements. The intended audience is primarily nuclear safety regulators, but government authorities, nuclear power plant operators and the general public may also be interested.

Good governance and efficiency in decision making by governmental authorities are increasingly dependent upon mutual trust and confidence between those authorities and the public. This workshop provided an opportunity to exchange information and views on how national nuclear regulatory organisations can improve their interface with the public.

Nuclear reactor safety is primarily concerned with the prevention of radiation-related damage to the public from the operation of commercial nuclear reactors; safety limits are introduced to avoid fuel failures during normal operation, or to mitigate the consequences of reactor accidents in which substantial damage is done to the reactor core.

In this report, brief descriptions of 20 fuel-related safety criteria are presented along with both the rationale for having such criteria and possible new design and operational issues which could have an effect on them. No attempt was made to categorise the criteria according to event type or risk significance.

This report will be of particular interest to nuclear engineers working in the area of fuel safety and to all those interested in general aspects of nuclear safety.

In recent years a world-wide trend has been developing to introduce competition in electricity markets. As market competition unfolds, it produces a wide range of safety challenges for nuclear power plant operators and regulators.

Nuclear regulators must be aware of the potential safety challenges produced and consider whether new regulatory response strategies are warranted. This report describes many of these challenges, their implications and possible regulatory response strategies.

The intended audience is primarily nuclear safety regulators, although government authorities, nuclear power plant operators and the general public may also be interested.

Major nuclear safety research facilities and programmes are facing increasing budgetary constraints, and in many cases are being closed or terminated. This report identifies major facilities of vital interest to the international nuclear safety community and makes recommendations for their continued operation in an international framework, either as joint projects or centres of excellence.

Major nuclear safety research facilities and programmes are facing increasing budgetary constraints, and in many cases are being closed or terminated. This report identifies major facilities of vital interest to the international nuclear safety community and makes recommendations for their continued operation in an international framework, either as joint projects or centres of excellence.

Irrespective of current views on the future of nuclear power programmes, concerns are arising with respect to the long-term ability to preserve safety competence because student enrolments in nuclear engineering are decreasing rapidly and experienced staff are reaching retirement age. "Assuring Nuclear Safety Competence into the 21st Century" was discussed in depth by workshop participants. The need for a long-term strategic view was emphasised, and policy recommendations were made. Thes proceedings will be of particular interest to those playing a policy role in the nuclear industry, regulatory bodies and the education sector.

The Incident Reporting System (IRS) is an essential element of the international operating experience feedback system for nuclear power plants. IRS reports contain information on events of safety significance with important lessons learned. These experiences assist in reducing or eliminating recurrence of events at other plants. The IRS is jointly operated and managed by the Nuclear Energy Agency (NEA) and the International Atomic Energy Agency (IAEA), a specialised agency within the United Nations system. This report highlights important lessons learned from events reported to the IRS over the period of July 1996-June 1999. A total of 342 events were reported by the participating countries during this time. Several areas were selected in this report to show the range of important topics available in the IRS. These include several different types of failure in a variety of systems, as well as experience of human errors in combination with system failures. It is important that sufficient national resources be allocated to enable timely reporting of events important to safety, and to share these events in the IRS database. This report is intended to provide general information for senior officials in industry and government who have decision-making roles in the nuclear power industry.

Since 1998 the NEA Committee on Nuclear Regulatory Activities (CNRA) has been dealing with the issue of how a regulatory organisation can recognise early, and address safety performance problems that stem from, safety culture weaknesses. Following a report published in 1999 entitled "the Role of the Nuclear Regulator in Promoting and Evaluating Safety Culture", this report explores regulatory response strategies for dealing with declining safety performance. It also discusses resumption of normal surveillance after a period of enhanced regulatory attention and intervention.The intended audience is primarily nuclear safety regulators, but government authorities, nuclear power plant operators and the general public may also be interested.

Major nuclear regulatory challenges will arise from government policies to liberalise energy sectors. In a context of growing competition and market deregulation, it is becoming increasingly important to reconcile commercial interests with safety requirements. For nuclear regulatory bodies, the first challenge will be to ensure that economic pressures do not erode nuclear safety. In their strive to maintain nuclear safety culture, regulatory bodies will also need to adapt to an increasingly market-oriented environment and new working relationships with operators. This report identifies the challenges that regulators are likely to be confronted with over the next ten years.

Even though there is an internatinal consensus on nuclear safety research needs and objectives, there is a strong concern about the ability of the OECD Member countries to sustain an adequate level of research. In this publication, senior experts discuss existing and planned capabilities and experimental facilities to fulfil needs identified in two previous publications: Nuclear Safety Research in OECD Countries and Nuclear Safety Research in OECD Countries: Areas of Agreement, Areas for Further Action, Need for Collaboration. Practical means are proposed here to address the concerns

The OECD Nuclear Energy Agency co-operates with both the central and eastern European countries and the New Independent States of the former Soviet Union in planning and executing safety research programmes. The purpose is to build up know-how and capabilities in safety technology pertaining to their nuclear power plants. In this report, senior safety experts from Russia and Western countries review the nuclear-safety research needed to improve the safety of Russian-designed nuclear power reactors. They have selected a number of important research topics to which priority should be given. They have also identified nuclear-safety research topics that would benefit from a collaborative effort between eastern and western nuclear-safety researchers.

Many countries have progressed in their work on implementing severe accident management programmes. In this report, senior experts analyse and integrate the results of severe accident management research and implementation to date by describing the major decisions associated with severe accident management, the remaining open items and areas of uncertainty, and the status of implementation in OECD countries.

The international nuclear safety community shares a range of specific concerns. Continuing research is necessary to address many of them. In this report, senior experts discuss research areas of special importance for safety and regulation, safety research areas for which a common technical position exists, areas for which further discussion is needed in order to achieve a common technical position, and areas to which priority should be assigned.